Preheat your oven to 400°F.

In a large stockpot, bring generously salted water to a boil. Add the uncooked whole-wheat rotini pasta and cook until al dente.

With one minute left in the pasta cooking time, add the broccoli florets.

Once cooked, drain the pasta and broccoli and set aside.

Heat a sauté pan over medium heat and add the butter or olive oil. Once heated, add the sliced onion and sauté for about three minutes until it begins to soften.

Add the sliced baby bella mushrooms and minced garlic; continue to sauté for another five minutes until the mushrooms are tender.

Sprinkle the flour over the sautéed mixture, stirring well. Let this cook for about one minute to eliminate raw flour taste.

Gradually pour in the chicken or vegetable stock, mixing until there are no clumps. Add the milk, Dijon mustard, salt, and pepper, stirring until fully combined.

Bring the mixture to a simmer, then remove from heat and stir in one cup of shredded cheddar cheese until melted and smooth.

In a baking dish, combine the cooked rotini pasta, broccoli, the creamy mushroom sauce, and the cooked chicken. Toss gently to ensure everything is well coated.

Smooth out the mixture into an even layer for baking.

Bake uncovered for 15 minutes. After this time, sprinkle the remaining cup of cheddar cheese over the top and return to the oven for an additional 10 minutes until the cheese is melted and bubbly.

Remove from the oven and serve warm. Optionally, sprinkle with freshly cracked black pepper or chopped herbs.